T&T - wrong end date given for isolation period?

[BillyWhozz]

Apologies if this is one of those that crops up regularly, I've done a search but couldn't quite get what I need and maybe someone has experienced the same.

DS14 tests positive on his lateral flow that school have been requesting on Monday 12th. PCR the next day, Tuesday 13th, also positive. Thankfully no symptoms.

Part of the text notification reads as:
You must self-isolate immediately for 10 days. This includes the day your symptoms started (or the test date if you've no symptoms and the next 10 full days) If this is a follow-up test result, self isolate for 10 days from the date of your first test

So to clarify what a follow-up test is I head to the Gov website.
If your LFD test was taken at home (self-reported), you should self-isolate immediately. You and your household members should follow all this guidance. You should also arrange to have a follow-up PCR test as soon as possible

So from that I interpret it that the test date was Monday 12th. So isolation is the 10 days following that, ending at 235 on Thursday 22nd.

However after a call from T&T talking through the circumstances above and giving details of the few close contacts he'd had, I receive an email stating
You have tested positive for COVID-19 so you must stay at home and self-isolate until 23rd of July (including this date)

I know it's only a day but am I correct or have I misunderstood the definition of a follow up test?

(Thanks for anyone that stayed with that!)

ending at 2359 that should have said, apologies

You isolate according to the pcr test or symptoms. not the Lf test

Thanks for the reply. OK, so what is a follow up test then if not outlined as above?

I think the LFT is a heads up that the person might have covid. PCR is a definite confirmation, so isolation starts from then.

Doesn’t make much sense though, if a person with symptoms can go from their symptoms start date not the test date, and effectively finish isolation earlier.

T&T systems are not good. If a second person in your household tests positive, a few days later than the first person, everyone in the household gets emails with the later isolation end date. Which is incorrect. So I wouldn’t worry too much about going out on day 10 as long as you’re not close to lots of people.

Correct procedure is here

assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/961291/Stay_at_home_illustration_Feb_2021.pdf

They were obviously positive on the day they took the LFT so I'd take that as day 0. I'd isolate for 10 days after that date