Latest I've noticed in a pin package is SK096 made in Malaysia with the L0 start to the FPO code, which is L for Malaysia and 0 last digit of year for 2000 ... I get the impression that the majority made this century were QFP rather than ceramic/pin.
I don't know how you'd tell a 94 from a 2004 straight off, I think they didn't start manufacturing in Malaysia until 96, you'd probably have to take other clues like that into account and text and logo styles.
On the other hand, I'm not sure what wear on the masters and other tooling is like over time. It has been said that semiconductors reach peak "tune" a year or two into manufacturing then it slowly declines. So if it was fully tuned up good as new in Malaysia from a commencement in 96 sometime with a fresh master then maybe 1998 would be the sweet spot.
edit: well I've just seen an L5 so obviously Malaysia plant got going earlier
edit II: saw some QFP trayed DX4-75s on fleabay, they had an LC at the beginning of the FPO number, so maybe after 0 they went ABC, so that might make those 2003? Dunno not come across a later year number guide.
editIII: Just got C5s SK051 DX4s here, so boring old 1995, which might be getting near the peak from that plant though since they launched a year earlier. However, there's some interesting things to look for Intel DX2 that are DX4s and AMD DX4s that are DX5s... https://x86.fr/the-odd-story-of-factory-downgraded-486s/
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
