You are way over thinking this.
Rolex advertise +2/-2 spd. There are no legal definitions, caveats, disclaimers or anything else about how that number is derived. Consumers therefore (in the UK at least as that's the law I'm familiar with) can reasonably expect their watch to operate within the parameters of either losing or gaining 2 seconds per day. Not operating within +2/-2 of a consistent loss or gain of however many seconds per day.
If I set my (up to 5 year old) watch at 1pm today to the exact time and its more than 2 seconds fast or slow by 1pm tomorrow using that same exact time reference its not operating within the spec Rolex say it will in their publicly promoted marketing information and I have a right to expect Rolex to address that under warranty.
Now, we all know that mechanical timepieces are subject to many different environmental factors, temperature, age of components, positioning, power reserve, wearing habits, etc, etc that can (and will) impact timekeeping, but the average consumer is not expected to know that and can, in law, simply expect their watch to perform as advertised.
Incidentally we also need to drop the whole precision versus accuracy point as far as Rolex’s advertising statement is concerned
Precision is literally defined as
“the quality, condition, or fact of being exact and accurate”
So there’s no difference from the legal perspective of interpretation of Rolex advertising.
I believe the laws are very similar throughout Europe. The rest of the world may of course differ.