Sometimes various changes in admission policies affect the app numbers and accordingly the acceptance rates. For example, in the case of BC above, if I recall, a few years ago the school added back in an app supplement that led to a decrease in apps and increase in acceptance rate. For class of 2022, the overall acceptance rate is back down to 27%. (The IPEDS lag: currently, IPEDS only goes through class of 2021 and won’t be updated for 2022 until next May or June.)
Some schools see decreases in acceptance rates after adding ED. Villanova is a prime example - 2020 rate was around 43%, dropped ino the 30s for 2021, and after adding ED for the class of 2022, the rate dropped again to 29%.