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@LEGO Historian Thank you for your reply! That's exactly the info I was looking for. I fully get the part about production end dates, specifically that there is no such thing ;-) So now I know that, e.g. my hypothesis that https://www.bricklink.com/catalogItemInv.asp?S=6335-1 from 1996 couldn't contain 2412a (grille tile without groove) is probably false. (Related question would then be to what extent can old parts be used in newer sets, e.g. could it possibly still happen that say in 2010 an old light gray (or even dark gray - which is much more different from the new version) part can be included? What are the limits where TLG can go here?) But now to the most interesting question to me. You mention that start dates for specific parts/colors are know (as I would expect). Can these dates be stated for the parts from my original post? Namely I'm interested in the first year following parts appeared: normal (smooth) tiles with groove special grille tile with groove various versions of clipped plate 4085x minifig heads with blocked open stud new parts without Pat.Pend. text or with dimples on studs (instead of on side)

@LEGO Historian I've just recently read some of your posts and your amount of knowledge really is impressive! Perhaps you could shed some light on the issues described in the first post of this thread. Thank you

Well, the thing most interesting to me is actually the year when a mold appeared first in production. I understand that having detailed data for each set might be difficult but I would at least like to have statements such as "production of 4085b started in 1984 and therefore all sets before that claiming to use it are mistakes". Can someone make similar statements about the parts mentioned in the original post? How do you know that it was not used after 2017, i.e. what is this information based on? Brickllink? Rebrickable? How do you (or who knows) that it is correct, esp. for older sets?

Also does Bricklink differentiate between new and Pat. Pend. parts? I couldn't find that info there.

I haven't consulted Bricklink but it seems to have the same functionality as Rebrickable, although it sometimes gives different info, e.g. https://www.bricklink.com/catalogItemInv.asp?S=6335-1 is listed as using 2412a which I pretty much doubt in 1996. So the problem is not that I cannot see year ranges. Both Rebrickable and Bricklink provide them. What I question is their reliability, i.e. whether anyone with more knowledge than me can confirm (or correct) the data. I should probably have stressed this more.

Hi all, this is my first post here on Eurobricks so I would like to take this opportunity and greet everyone out there! I'm out of my dark ages for 3 years now and slowly I'm collecting and building the sets I wanted to get in my chilhood (but there wasn't enough money back then...), majority of them from the 80s and 90s (plus some newer Technic sets). I manage my collection on Rebrickable and I'm trying to keep detailed track of every Lego set and part I own or got lost from a set. Since I get all my sets from second hand and often in big unsorted collections (I somehow enjoy sorting those collections into sets cleaning the parts along way :-)) it sometimes happens that the parts are not in great condition anymore and/or are of different color/mold than what was originally included in the set. The most frequent example in the period of my interest (80s and 90s) would be tiles with or without groove. And now comes my question: What were the transition periods for different colors/part molds, i.e. what was the first (and ideally also last) year the specific part mold/color was used in a set? AFAIK with gray color variations it's quite easy: old gray colors were exlusively used till 2003 while the new ones exlusively since 2004. But can similar statement be made about part molds? Up to now I was relying on what Rebrickable lists but I'm starting to doubt it as there are clear mistakes (at least from my experience). For instance I doubt that the special grille tile with groove was already in production in 1990. It's more likely that it appeared only in 1993. Here is the list of parts of which I would like to know the transition periods for (or at least definitive year of first production). If someone has knowledge or interest in this topic feel free to extend the list with more parts: Generally all tiles which can come in variant with or without groove. Currently it seems that normal tiles were intro duced in 1976 and in 1993. Can anyone confirm these dates? In both cases it's highly probable that even after those respective years the older variants without groove were still used in some sets, perhaps even inconsistently in different copies of a single set. I'm sure that someone knows the answer for the first date. The question of the last year of usage of any of these parts might be much harder, though. Plate special with clip, e.g. . Here I have no clues about the three 4085 molds. It only seems for sure that the "d" mold started to be used much later in 2007 and that 4085a is not used anymore. Minifig heads with solid or blocked open studs. Here I'm again not sure but the newer variant probably first started to appear in early 90s (perhaps 1991 or 1992?). Parts with/without Pat. Pend. text and/or the dimple on side/on stud. These seems to appear in the older sets before 1978. This is probably the most tricky question, also given the fact that there actually is no official differentiation between these on Rebrickable. Also some of the parts, esp. those one stud wide have no place for the Pat. Pend. text so currently I identify them only based on the position of the dimple. Is this reliable method? Also here the transition periods are especially unclear. Given the very low number of old (pre 1978) sets I have the variants with dimples on sides appear much more frequently in my collection than what I would statistically expect. For instance just recently I was sorting out pieces for 2 pirate ships from 1989 which came in mixed together. The mix contained 18 1x3 black bricks and all of them were with side dimples. Of course this might be pure coincidence (the previous owner could have used parts from much older sets here) but this was definitely not the first time I saw something like that. I hope the community here can help me cracking this difficult problem :-) Cheers