Tasha Yar said that to Picard when they were onboard the shuttle flying to Enterprise docked in drydock and it was in 'All Good Things' I think.
And that would be logical, every ship should have ability to separate saucer section from stardrive when drive is too badly damaged but they wouldn't be able to reintegrate cuz they're not connected with maglocks like Galaxy or Prometheus. I read somewhere that during separation, microcharges explodes throughout neck connection to saucer, airlocks are sealed and stardrive dissconnects from the saucer (which is now only running on batteries without warp capability and limited impulse power - due to lack of either main or auxiliary power units) This would mean that Galaxy was indeed the first ship to separate, Constitution ejects/severs half of the ship permanently.