I had to do recovery today which on Xperia 10 III means flashing the recovery and then flashing back the boot image after you’re done. Per the instructions:
You will need the same version of hybris-boot.img as belongs to the Sailfish OS version of your phone currently.
I’m on 5.0.0.73 and I cannot download that so I flashed one I had lying around (5.0.0.71) but I’d prefer the 5.0.0.73 image, except it’s not in the Jolla Shop download page. Is there any way to download early access images?
They never released an EA-Image. But as far as I remember they are published when the update is released for all.
Huh. Good question. Let’s hope some dev sees it.
I don’t use on-phone EA, and I never saw an early access image anywhere.
That said, if it worked, it worked 
I doubt there are any differences between any of the 5.0.x.y variant boot-images (for the same device). You could check if the 5.0.0.71 boot-image is different from any of the previous 5.0 boot-images.
Might be true and seems to work fine, but one day that might not be true and I’ll be left with a bricked device, even if it’s only temporary.