Web of Spiderman #19 is also the 1st appearance of Solo.
I’m surprised we didn’t have this in Core! Has been added, along with ASM Annual #24 (1st solo story) and Spider-Man Vol. 1 (1st cover app). Thank you for letting us know 
Solo is pictured on the cover of Web of Spider-Man 19 as well, just not in his current costume.
hmmm that makes it a bit more complicated. I’ll just remove that one