https://www.parl.ca/DocumentViewer/en/45-1/bill/C-12/royal-assent
I think subsection Immigration and Refugee Protection Act 101(1.1) has to be read together with the condition at the start of the sentence.
It begins with: “if the claimant has entered Canada more than once after June 24, 2020”. That phrase limits the entries being considered to those that occurred after that date. When the subsection then refers to “their first entry”, it is referring to the first entry within that group, not the person’s lifetime first entry.
So if someone entered Canada in 2018 and later again in 2021, the 2018 entry falls outside the scope of paragraph 101(1)(b.1) because that provision only applies to people who entered Canada after June 24, 2020. In that situation, the 2021 entry would be the relevant date for calculating the one-year period.
Of course, the final interpretation will ultimately depend on how IRCC/CBSA apply the provision, and potentially how courts interpret it.