Type I photos ... I think ... wise to slab or not?

[BlackwellAuctions]

New to forum, so I hope this is posted correctly.
I've acquired a box of press photos, mostly 1940s-50s baseball, from the estate of an AP sports reporter (worked there from 1943-71) who died in the mid-1990s. Quite a few have dated captions/releases pasted on the back and stamped with AP Newsphoto (not Wirephoto) stamp, and are clearly proper photos from negatives. Are these necessarily considered to be Type I? I'm trying to determine whether or not the better ones are worth sending to PSA. It seems that the photos that command significant premiums of any kind are all slabbed. I'd be grateful for any recommendations.