I've noticed in the last few years that my 100 SCM breastroke can vary by over 3 seconds between practise meets (as I'd call them) and nationals (therefore 5-6%).
My team mates don't vary so much. I've also not yet done a PB/PR in my main events outside of Nationals. I'm usually happy to get 'in the ballpark', which is a vague range of a couple of seconds depending on when I'm swimming.
I put it down to more of a willingness to race tired during the rest of the season, which not many of the masters I know will do. For example, on Saturday I swam 200 IM, 100 *** and 100 free in an evening session for the training effect, 48 hours after doing weights then lactic tolerance (which was a complete meltdown!). Most of my masters team mates would back off even a small meet / time trial to see what they could do.
Even though my training programme is not all that heavy, I still make sure that I taper over a good couple of weeks - spending time at race pace but ensuring recovery (particularly in the last week).
What's your approach to racing and tapering and how much do your times vary over the season?