7, rarely 8 (it does happen occasionally)for all sirtalis'. If you see 8, then much of the time, on sirtalis' there's 7 on the other side.
I see 8 too. Try the other side. If you still see 8, then the inter nasal scale shape can be used to tell sirtalis apart from elegans. Plus, on elegans, the 6th and 7th aren't as enlarged as they are on sirtalis'.
Yes. occasionally a snake will have 8 instead of 7, but in my experience, the extra scale is usually just on one side. An extra upper labial on one side happens in other species too. I'm sure theres a few T. elegans' out there with 9 on one side instead of the usual 8. I've seen quite a few northwesterns (t. ordinoides) with 6 on one side, 7 on the other.