Previously (in 2016, IIRC), while they were working on the west side tracks, the New York section followed a different route and terminated at Grand Central instead of Penn station. The other Empire service, Adirondack, Maple Leaf, etc. trains (those that follow the Hudson River to Albany) did the same. This past summer (2018), while they were rebuilding the Spuyten Duyvil Bridge, the other trains again used GCT, but the LSL New York section was completely eliminated.
Nope, completely incorrect. Not a single Amtrak train served Grand Central in 2016. In the summer of 2017, certain Empire Service trains served GCT, and this summer (2018) all Empire Corridor trains except the LSL served GCT. The Lake Shore Limited has never in recent years years served Grand Central, mainly due to its inaccessibility from Sunnyside Yard, where the train is turned, serviced, stocked, etc.
So, I had the year (which I qualified with "IIRC") wrong, which made the entire post incorrect? I rode the Boston section of the LSL to/from Chicago in August 2017, among other times. Once when I took it (possibly this 2017 trip, possibly earlier), the New York section was an entirely separate train. I'm sure there was no sleeper service and maybe no dining car, just coaches on the separate NYC train. The NY passengers had to transfer across the platform at Albany to the Boston/Chicago section. They may have added and dropped the normal NY sleepers and coaches to the Boston section at Albany. Those cars presumably stayed overnight in Albany and returned to Chicago the next day (or maybe even the same night if the scheduling worked.) Since there were only coaches to be turned around at GCT, the lack of access to Sunnyside wouldn't have mattered.
I am certain this train was listed on the schedule as the LSL and made the various stops along the Hudson River at or close to the normal LSL schedule. For the NYC passengers, the differences were 1) they used GCT instead of NYP, 2) If they booked a sleeper, they had to ride coach to Albany before they could board their sleeper car, and 3) they had to physically leave the train and board another train in Albany. This situation was in effect for several months.
On a previous occasion, the opposite happened. There was normal 48/49 service to and from NYP, but the Boston section was coach only. If you booked a sleeper from Boston, you got Business class to/from Albany, where you transferred to a sleeper. The reason was the platforms and tracks in ALB were under construction and they didn't have room for the entire train or couldn't access tracks needed to split (eastbound) or join the sections (westbound), I'm not sure of the reason, but they were basically running the Boston section as a coach (plus cafe/BC car) shuttle. I booked the LSL BOS-CHI-BOS, but when I selected the tickets, my only choices were coach all the way or coach to ALB, sleeper ALB->CHI and the same back. This was the 2nd or 3rd time I rode the LSL, maybe in 2015 or 2016.
It was because of this previous experience that I was surprised last summer that they cancelled the New York section entirely rather than just do what they had done previously and just run it as a coach shuttle GCT<->ALB.