So I just sat down and read Destroyer Vol 3 myself, and wow, was that an ambiguous series. The only hint that it might be Earth-616 (and this is a stretch) is Cap's triangular shield makes a brief appearance in the Destroyer's workshop. It's left pretty open to interpretation.
I suppose the only way to know for sure is to get one of the softcover editions of the Official Handbook of the Marvel Universe A-Z. Those are second printings of the hardcovers that Marvel pumped out about five years back and they have "update appendixes" adding information that has been released since the original printing. I would suspect the entry on the Destroyer probably has that clarified in the updated appendix. I haven't been able to find a copy (I'm also at odds about buying all the revised editions since I bought all the original hardcovers, and paying over $20 per book for a few extra pages of information seems a bit outlandish)
But I'll keep an eye out, either way I think it's safe to list them as Earth-616 for now, I don't see anyone coming screaming down to have that corrected anytime soon if it is a mistake, and even then it's a pretty easy fix.
I know, right! I thought the same thing about the shield... That's the single shred of evidence that tangibly ties the entire series to anything Marvel, let alone Earth-616.
I also haven't seen a copy of that particular handbook, but may keep an eye out for it just to double-check. I have actually added the history to Marlow's page and created pages for all of the series' supporting characters and villains with an Earth-616 designation.
I really appreciate you looking into the matter for me! Thanks again!
It's nice to see you back. When you make edits to character profiles, I'd like to ask that you add in-line references. While you were away, the staff made some changes and have been pushing to get users to add references for all profiles on the site, to help solidify the information on the site, and help weed out bad info that may have been added over time. The link there explains most of it (although it goes off topic halfway down the page), but it'd be pretty helpful since you've been updating minor characters most people wouldn't touch on.
Sorry, I was unaware of the new changes to the site, though it does make sense and helps to make this site a better resource. I think that I have added all the appropriate footnotes to the character profiles that I have created or edited. If you see anything that I may have missed, just let me know and I will go back and fix it.