Perhaps the game had a little tweak in 88 and every copy made since had that tweak ?

Can you image it and open the image with 7zip to view creation date, modification date, etc ?

I don't know if it was ever a thing in the PC scene, but on other platforms modifying your floppy drive to ignore the write protect notch was a thing. I used to get recycled floppies for around a quarter of the price of new blank floppies - these came from duplication firms and had no write protect notch. Modding the target floppy drive to ignore the notch meant not having to cut notches on every floppy. I've had several such drives, but I never actually used one in an x86 PC.

It shouldn't be possible in PCs because the drive itself should simply ignore the write signal - as per the protocol specs. But the write protection works only if the drive has properly detected the floppy as protected. Many drives use optical barriers but some have mechanical switches for this task. A barrier should fail in protected state but the switch can get stuck due to dirt or corrosion - in that case it would read as not protected.

If the floppy disk drive is in working order, then the answer is no.

Apparently it is little-known that in fact the 3.5" drives can write to write-protected disks.
However, this is only enabled by a mechanism that is secret and has not leaked. It was established by the manufacturers when defining the 3.5" floppies and was intended for bulk mass copy stations, to avoid to have to manufacture special drives.
And this secret did not leak, it was NDA guarded well.

Before accusing me of spreading misinformation, I just say what the c't (reputed German computer magazine) wrote after their investigations.

Yeah, but OP didn't say if disks were 5"1/4 disks or 3"1/2 disks

^^ in this specific case it's a 5.25" disk, but I was more wondering in general.

I don't really think some super-sophisticated malware managed to get on there through the write protect (and then didn't reset the file modified date), I just thought it was weird. I can think of more plausible explanations, like someone on the dev team had their computer date set wrong. 😜

I can't answer this question on my own, but I believe what retardware said.
c't magazine was an accurate magazine and provided lots of low-level information
(I've got an UMB card for my XT clone that was designed by c't, for example).

The only thing I can really tell is that some 80s era software did know nifty tricks.
PC-Tools' PC-Backup/PC-Restore was able to detect a floppy change without any user interaction.

When it asked to insert the next disk, you just had to do so. No keypress was required.
I've never seen that before and after that (imagine MS software, like Windows Setup would have not required
key presses during floppy change. What a pjoy this would have been!)

Change detection can be done because there is a signal for this. But it might not be reliable - in theory /DSKCHG should go low when the new floppy is clamped and drive is selected, but the clamp sensing is mechanical. If you somehow mess up inserting the floppy and want to redo, the program might already detect the signal and start R/W operation. That might damage the floppy or the heads.

I've never heard of this secret method, as I see it the mod to bypass the write protect sensor would be trivial. But it's possible I guess.

I've also heared that this detection feature was planned for Windows 95 but never ended up in the final product because some floppy disk drives makers wired these the opposite way, and that there was no way to detect which variation of the disk drive you had, so it was scrapped.