From past experience I have found that most of the schedules continue in effect after 21 May with increased service (if anything) to popular destinations for the tourist season. You should be able to make your plans based on schedules currently in effect.
Trains often don't go as directly as one may wish. For example: Whether you are going to Ourense or Oviedo or Santander from Madrid, the train route goes thru Medina del Campo. You may also want to fill in with travel by Motorcoach: Several Bus Companies have very comfortable (and often more convenient, more frequent or faster than Train)Business Class Motorcoaches, seating 3-across with on board attendants to serve food or drinks, restroom equipped with express service between major cities. Try
http://www.alsa.es and look at their 'Supra' service.
[ 04-17-2001: Message edited by: Antonio ]