You may want to research the Building Science literature on off-gasing
of formaldehyde from manufactured building products. It has been awhile
since I was involved in that area but if memory serves me correctly (a
less frequent event as I age), exterior grade plywoods use a glue
formulation that does on off-gas formaldehyde as readily as interior
grade plywoods. There may also be an issue with any other VOCs
(volatile organic compounds) which may be present in the glues. You may
want to obtain a material safety data sheet for the glues used in
manufacturing the plywood if available. VOCs will off-gas over a period
of time (temperature and humidity dependent) so I suspect that your
older frames should not pose any problem.