FLR(M) - Items of Correspondence - Confused over period

I am a British citizen with an American wife and we're living in the UK. My wife’s initial 2.5 years leave to remain in the UK as my spouse expires on 28 July. We’re hoping to apply from within the UK for an extension (FLR(M)) as early as possible in July.

I am confused by UKVI's wording of the requirement for items of correspondence:

"Items of correspondence addressed to Mrs X and Mr X at the same address as evidence you have been living together since your last grant of leave in this category, or from the date you first started living together, covering the last 2 years".

Should our correspondence cover the whole period since the last grant of leave to remain (2.5 years ago) or should it just cover the last 2 years?

Pretty sure that it is 2 years that they want correspondence for, not 2.5. When we applied for our second FLR(M), we provided 2 years, even though the prior visa was for 2.5.

6 joint items or 12 individual items evenly spread over the last two years.  Or a combo of the two.  For example, 3 joint items and 6 individual.  Just make sure they are evenly spread, from "official sources" and from the same month if individual items.

It's definitely the most painful part of the application.