I'm not sure if it still happens but when the RAF reverted to using QFE many years ago after using QNH for a couple of years, they also abandoned use of local QNH, and their met forecasters probably don't even bother to calculate it now, so this would explain why IO540 couldn't get it from Shawbury.
System used was (and may still be) you departed on QFE, and changed to 1013 at TA; inbound at TL you changed back to QFE. If you ever went anywhere below TA, you set RPS.