With megapixels these days, it's always noticeable... :-(
Getting the best results out of any given lens when shooting the night sky is definitely the biggest challenge/frustration I've ever faced. No matter how sharp a lens is proven to be "on paper", it can all fall apart if you miss focus by a fraction of a millimeter, (especially on modern AF lenses with abysmal focus throw) or if you heavily abuse your lens for a few months or a year, and something gets even slightly out of alignment. GeekyRocketGuy and I have seen many of our Brokinon lenses pass away in the prime of their youth from such a common ailment. :-P
Even on my test images from the A7R3 and the 24 1.4 GM, I have some examples of f/1.4 perfectly nailing focus on stars through the entire image or plane of focus, ...and a few images which inexplicably have a soft right edge despite being tack-sharp in the center, or even being stopped-down to f/2.8...
And nowadays, there's even more variables that could be the culprit. Did the IBIS lock the sensor at a slightly skewed angle when turning it off, causing a tilt-shift look to those few images? Or did I simply miss focus?
I've resigned myself to starting my manual focus workflow somewhere between the rule-of-thirds points and the extreme corners, trying to nail focus there, and then checking the dead-center and the other corners. Because no matter how perfect you think you've nailed it in the dead center, there still seems to be some small %% difference in the depth of field (yes, even at f/1.4 and focusing on stars) between dead-center and the corners, so you just can't be sure unless you actually check.
I hope Tamron is working on more f/1.4 primes, whether for DSLR mounts or mirrorless mounts; they seem to be onto something good. Or maybe 35mm is just that much easier to do well than 24mm or 35mm, as we found with the Sigma 20, 24, and 35 1.4 Arts. I guess we'll find out.
Then, there's the "fact" that Sony's FE mount is the narrowest diameter of the big three, so if we really want to see something impressive, we should all wait until Nikon puts out their (alleged/leaked) 35mm f/1.2 for that gaping maw of a mount they have now...
Oh, and if LR needs an astro-focused review of any of these lenses, I'd be happy to communicate with Zach S. or anyone about that. :-D