Glacier Express

There are 2 that day. Sounds more like they just are not taking reservations until tickets go on sale.
However, when I look at the site, the 9:15 looks fully booked, and the 10:19 has 1 seat in 1st class. However they are only showing 1 carriage in each class. When I look at Tuesday, the 18th, there are seats open, but only showing 1 carriage in each class.
I suggest you email them at the contact shown at the bottom of the reservation page. They will get back to you next business day. They may be holding carriages in reserve and more seats will open up.

Thank you. Waiting to hear back from my email. Looks like there is availability from Chur to Zermatt on my travel day. If we take a regional train to Chur from Pontresina will we miss the best part of the glacier Express? It looks like regional trains are 2 hours and depart frequently.

You don't miss anything. The mountains look exactly the same. The railroad tracks of the Albula line take the same spirals and curlesques through them.

Good to know. Sounds like that will be an option if reservations don’t open up. Another common question, half fare card or Swiss travel Pass? We will be taking both the Bernina Express and Glacier Express, as well as trains from Zermatt to Wengen, Wengen to Lucerne and many of the funiculars, cog wheel and lifts including Jungfraubahn, shilthornbahn etc. over 12 days. Seems like the 15 day STP is the way to go.

Also what about Berner Oberland pass? Will be there 4 full days.

The Berner Oberland Pass on top of a STP or HFC is just donating money to Swiss railways. You have to price out every journey, noting what each product covers, to get a rational answer. Usually, the HFC saves the most. An STP might work, and there are a few benies, like convenience, museum entrance fees to give it a nod if it is close to the HFC.

If you are taking the Bernina Express, it goes to Chur as well on the same tracks as the Glacier Express with panorama cars. Why not stop there instead of St Moritz?

Heard back from Glacier Express, they suggest alternate journey of St. Moritz to Brig, which has availability on a 7am train but a 1 1/2 hour layover for the regional train to Zermatt arriving at 4pm; or regional train to Chur then Glacier Express to Zermatt 2pm departure and 8pm arrival. My question is which option sounds better, is there anything to do in Brig or Chur near the train station during the layovers? They also mentioned there might be more seats opening up on my original preferred route a month prior, but now sure how/if reservations transfer, or if it is worth the risk waiting, any ideas?

We took the Glacier Express route from Andermatt (we were traveling from Luzern-Interlaken that day) to Chur on a regional train because the Glacier Express had no seats left. Same breathtaking views. No additional charge, barely anyone on the train. Don't waste your money, unless you really want the tablecloths and china and a meal. For us, a baguette and a less crowded car were perfect.