It was changed when they made escorts part of the new quest system in Mondain's Legacy.
Before then, you could escort as many regular escorts, and as many rescues as you could get.
The downside was that some of the quests wouldn't work right. For example, you could only get escorts wanting to go to "any dungeon" (or rescues found in a dungeon out of it to their destination) with Gate Travel, due to the orientation of the server lines (crossing in or out of the dungeon through an entrance was not a straight line but a jump to the "black" areas you see in UO Automap, where the dungeon interiors and T2A were put). Occasionally, the same would happen trying to go through a permanent moongate in a direction opposite your line of travel. If you got too much room between you and the escort following, they could despawn when you crossed a server line, and if they were stale (near despawn at the time they were picked up), they could disappear when you crossed a server line after their original despawn time.
Some people even claimed it was impossible to go across ANY server line with an escort - and i was called a liar when I proved them wrong and provided screencaps as evidence.
- I picked up FIVE rescues on Trinsic Barrier Island (that, alas, no longer occur there).
- WALKED them to Britain, dropped one off, acquired an escort in the middle of town. (back to 5)
- Picked up another rescue somewhere between East Britain and the Compassion Crossroads (up to 6)
- Delivered 1 of the 6 to Cove. (down to 5)
- Delivered 2 of the 5 to Minoc (down to 3)
- Lost one from probably staleness crossing the server line by Minoc gate (down to 2)
- Finished the delivery by getting the last 2 to Vesper.
So I had as many as 6 escorts at one time (7 total), and delivered 6, only losing one.
And, I had fun WALKING them there (character was a paladin on a swampy), fighting more brigands on the way, and stuff attacking me along the way. 10-15 minutes after I started, I had all 5 compassion gains for the day, plus a spare that I just got gold for.
I REALLY wish that was brought back, just with the crossing fixed. For that matter, they could redo the brigand (with or without prisoner) and other non-gypsy special spawns (wasn't there one with evil mage/cultists and a sacrificial prisoner to rescue?) with something similar to the Trade order ambush code - just not requiring you to be on a quest, just that a PC was passing through a specific area of a subserver.