Is a23 the same as 23a?

Yes, A23 and 23A are the same battery.

Do these replace an A23G battery?

Found by asking this question on the page with the A23 batteries. Q: Do these replace an A23G battery? A: Yes. That's what I bought them as replacements for. By Jim from MD on January 2, 2021 Q: Does this replace the L1028 battery A: YES By Amazon Customer on April 2, 2018

Why did I not get A23 Alkaline batteries and they were not in a manufacturers packaging?

You will have to contact the source. Sounds like they broke open a large pack to ship individual units. Makes it touchy since you don't have the expiration date.

Do these come in lithium? Also, when I put a new one in a batt tester it showes 100% and then dropes down to "bad" in under 10 secondes. Why?

I didn't test them. I just put them in both my bedroom & living room fan/lights and they are still working. I have had no problems with these replacements.