Is It British Guiana Sg 222A ?

Is this the "without dot" overprint variety? Thank you in advance for your opinions.

Maybe, you should first check whether the overprint is genuine. It looks a bit too neat compared to the image in the SG catalogue and that of an online catalogue.

Original from Wikipedia

That picture from Wikipedia looks much like the one in the online catalogue. The overprint is very different from that on your stamp.
I would hesitate to assume Wikipedia is showing the genuine overprint, but, at least, it raises the question whether your overprint is genuine.

The overprints were done in settings of 60, 6x10.

I don't have any scholarship newer than about thirty years ago, but it was thought that the two higher values were set twice, and this value was set once, probably after the other two. There is a fair amount of variability among the 60 positions. The "stop omitted" appeared at position 53, but not in every position 53, apparently.

If you can find images of multiples from the lower right corner, you can see what the lettering looks like at position 53. Whether there is a stop or not in the multiple you're using for comparison, your letters should match. Position 53 would be the next-to-last stamp in the next-to-last row. Again, probably obvious, but you need to be comparing with other examples of this value, not the two higher values, to be sure.

As always, if someone has newer information or differing interpretations, speak up.

I did a little more flipping around, and I ran across Michael Nicholson's note in the BWI Study Circle Bulletin 167 from December 1995.

He claims that the correct position is #9 (Row 2/3, i.e., the third stamp in the second row), and he cites very old sources claiming that the stop was eroding during printing, such that you often only see a tiny remnant of the upper portion of the stop.

Interesting stuff.