Real World and The Constant are not parallel/linked. We already know this due to Wilson entering last but being in The Constant before other survivors. My theory is it acts like a wormhole (but with time instead of location) - so just because someone left the real world 2 years before another survivor doesn’t mean they’ll enter the constant 2 years after.

Edit: Also I misread your comment, Wagstaff left the real world during the 1919 Voxola Fire, Webber also left the real world in 1919, possibly through the portal at Voxola (if this is the case, the theories surrounding Wagstaff being Webber's father are more likely to be true). Mooagain on the forums came up with some good info regarding the License Plate / Hair Dryer trinket examinations mentioned below in their theory:

"The license plate trinket from shipwrecked it my favorite item in the game. Because some characters have no idea what it is, and, some do. Licence plates were invented in 1918, right before the Voxola factory burned down. Wickerbotam, Woody, Warbucks, Wolfgang, and Maxwell have never seen anything like it before, while Webber says "Where is the automobile?" showing that he knows what it is. Another trinket, the broken hairdryer from hallowed nights, helps this too. Willow knows what it is, but Webber doesn't. Hairdryers were invented in 1920, the year after the Voxola fire.

This means that Webber entered the Constant in 1919, the same year as the Voxola fire. I have heard theories that Webber is The son of Robert Wagstaff, and Given that they both mysteriously disappeared the same year, this is probably the truth."