I thought I've had this coin long enough to post it in the 3rd edition. But apparently not - or at least not with pics.
(Bigger surprise: I didn't remember to post it in the 4th edition either. I've definitely had the pics by then.)

Tsardom of Russia, Peter I (the Great)
AR kopek, (7)208 AM = 1699/1700 AD
10x7 mm, ~0.3 grams; I probably took a more precise weight but forgot
[if I ever figured out its KG variety number I don't remember it]
This is the coin type that (AFAICT) features the highest numeric date ever represented on a coin: in the local calendar of the time, this coin was issued in the year 7208.
The date is given, in the Russian version of the Greek alphabetical numerals, by the letters CH, which correspond to 200 and 8 respectively. The 7 thousands were omitted - a common practice at the time.
(Yes, this technically means that the date is incomplete, and puts a cloud over its status as the largest. AFAICT, as I write this, the largest
complete date represented on a coin is 5783, on
this Israeli NCLT piece. I'm also excluding date mistakes, some of which had gone into five digits.)
The calendar was officially changed on 1 January 1700 AD, so I'm assigning this coin to 1699 even though the year 7208 AM nominally ended on 1 September 1700 (i.e. was mostly in 1700).
IIRC sources differ on whether the minting of this type had in fact continued into the newly renumbered year (and if so, for how long).
I've made an extensive write-up on my interpretation of the minting of this coin in
its Fifth Edition entry.
(I thought that write-up was actually posted in another thread - and indeed it originally was, but the original version contained some very unfortunate errors that were fixed in this version.)
...As usual for my pics from this period of my CCF participation, I apologize for the rotated photos; they were the right way up when uploaded, but a glitch in CCF's treatment of photo orientation added a 90 degree rotation (many years after upload) to all phone pics I uploaded to CCF for several months in 2016-17.
I have another coin from 1699 (which AFAIK hadn't been posted in a HFBCWG thread before, though I've owned it even longer than this one), and I hope I'll be able to post it later today.