OK to leave some "gunk" on front display edges before reattaching?

I’m putting my iPad Air back together after having replaced the battery, following guide 25869. I’m at the point where very shortly I will be re-attaching the front display (the piece of clear glass, a.ka. “screen” or “digitizer”), then re-attaching the LCD, then putting the pre-cut adhesive onto the frame so I can press the front display back into place.

The frame is quite clean - no black adhesive tape; I am down to bare metal on the edges where the new tape will go. The front display (the glass) is also clear of tape on its edges - however those edges still have a very thin, very spotty layer of black "gunk,” i.e. adhesive residue. The instructions say to “clean the remains of the adhesive” from the glass with isopropyl alcohol - but I am finding this simply doesn’t do the trick, given I am restricted to plastic scraping tools if I wish to avoid doing damage. An alternative would be to buy a new front display, but at $39.99 from iFixit that’s pretty steep for replacing a part that is not actually broken.

My limited experience w/ iFixit repairs (I’ve worked on a couple of Macbooks & an iPod) tells me that as long as the gunk is merely a very thin layer, and is itself clinging quite tenaciously to the glass, that this ought to be good enough for the new adhesive to adhere. However, there is another aspect: would there be any chance that a minuscule increase in spacing between glass & LCD would interfere with touchscreen function?

I guess I could go ahead & see; and if there were interference w/ the touchscreen, I could shrug, buy the new front display, & do a follow-up procedure to install it. At least it would be simpler than the full battery replacement procedure I just went through.

For those of you w/ lots of experience fixing tablets etc., what do you think?