It's not unusual if only a small number of records were expected to be sold. Previous on the label (B.B. King) came also in this same combination.
The EMI 1A catalogue numbers date from 1979 or later. 5C numbers were used from 1969 - 1979
Very odd - not just for the US cover with a Dutch record (was it really released that way, or is either the cover or the record a replacement for a damaged original?), but for the fact that the record doesn't use EMI's then-standard European style of catalogue number, which, based on other European releases shown in Discogs, would have been something like 1A 062-93752; unfortunately there's no Dutch entry at that site.
EDIT: Didn't see the other Dutch Probes linked below - those have 5C as the prefix, rather than 1A.
EDIT 2: Turning my brain ON (I know, I know....) maybe EMI intentionally used the Dunhill catalogue number so that it would match the imported cover! I wonder why they couldn't have printed the cover themselves, though? It's not like this was a major band.
What we have here? A nice thick US Dunhill gatefold sleeve, Probe labels with Made in Gt Britain, but with STEMRA as rights organization. Adding records requires putting your brain ON.