First time issue for me after 26 years as an FFL, figured someone might know

Had an Erma Werke competition pistol show up with a spare slide in another caliber.
As with many European guns, the slides are serialized, not the frames
I was under the impression that to be imported, the guns had to have the frames serialized, along with the importer information
I see no frame numbers, no importer name, etc.
Anyone ever dealt with these guns in the past to maybe shed some light on this issue for me?
It got some of the oversized wood grips so maybe there's something hiding under those, but I don't want to disassemble it if I don't have to.
The gun isn't pre-'68 that I know of, if that matters

That is true. (Unless possibly the post-68 importer had some special variance, which isn't something I've encountered).
GCA 68 only requires the s/n to be on the frame. The importer name and location could have been on the slide or barrel.

Did this particular model exist prior to 1968?
I'd remove the grips to look, or ask the transferee to remove them if they have availability prior to the transfer, if they're confident in that task.

Was the transferor a FFL? If so, ask them.

The customer took the grips off in my presence.
The transferor was an FFL and listed the gun by the number on the slide in their paperwork to me and the buyer.
I did find an importer name on the mag well in very small print.

Model ESP85A Wiki says it was made from '88 to '94, so not as old as I had presumed.

Here's a possibility.

I was stationed in Germany, 89-90-91.   I brought back over a dozen firearms on ATF Form 6s.  They came back as marked, of course.  No import marks, no changes to how serialized.  ATF doesn't ask for or look at pictures.

Many firearms in the US brought back by US Servicemen.

Absolutely.

I believe LE may also import on Form 6 for official use (bypassing any licensed importer, along with their engraving requirements).

Good thinking.

Yep. I know MSG posted in pro-gun places like SA who brought back dozens. All legal. Unfortunately I was only sent to anti-gun shitholes and either no access or the guns I did have access to were illegal to bring back (AKM, etc).