Currently if a player leaves a Fellowship during the Spire of Eternity any points they earned while a member of the first Fellowship stay there, any new points will go to the new Fellowship. They will receive the prizes only from the new Fellowship and provided they complete 1 encounter there. There has been some discussion about changing this to be more similar to the Fellowship Adventures, so while this is the case now, it could certainly change.
I have very good reason to believe that this is not correct. If this were truly the case. in our situation,we should have received surplus rather than a deficit a member left with more points than the member that joined during the Spire had when they joined.
Support did not provide this information despite my directly asking if this is the case. They did say that all the points of any member that left mid-spire were lost. The evidence I have indicates that this is indeed true.
Based on the information provided, the data observed and my experience programming I believe the algorithm used to assigning Spire points is simple counter increment routine that applies points earned from a completed encounter by each to a Fellowship's total. This is fine as long as the point from members that leave are not deducted and this activity is clearly documented in the Wiki. This is fully supported by the data I collected (We track FS Spire activity closely and I have built a comprehensive spreadsheet to enable me to determine what combinations are needed to reach Gold in a given week). I surmise, based on other threads, that a change was made after complaints that some Fellowships were earning more than 1575 points in a week because when members left, their points stayed behind leaving the Spire open to the same sort of abuse of the system by rotating members in and out of a Fellowship that was addressed in the FA rules change. Since the limiting factor in FS Spire play is that each member can only contribute a max of 63 points. I was told repeatedly buy support that the system deducts the points accrued by a member from the FS when they leave.
The effects of players, leaving and joining mid-Spire (and mid-tournament for that matter because I found nothing by speculation on that subject as well) need be properly documented, put into the Wiki and FAQs. Additionally, Senior Support should be aware of this and provide a consistent response
with details for deviations of official FS points totals from a summation of individual points earned by members. For example: player A left on given date with X points, this was deducted. Player B joined on given date with x points These did not transfer to your FS, They earned z points.while a member and these were applied to the FS total. This clears any confusion. This is nothing like what I got from Senior Support, which simply stated repeatedly, "your points total is correct" and in one message stated that 7 members hadn't made it to the top of the Spire, while I could see that all but 6 did before that statement (which was a factor in my conclusion that a simple increment routine is used and individual score is reset when a player leaves a FS and additionally that the view presented to support is not the same as that presented to players.)
I suspect that the number of people to actually notice the anomalies, I've reported are virtually nil. I have over 40 years experience in Information Technology, on the Autism Spectrum and frequently end up discussing anomalies I find in the Enterprise applications I manage with product engineering because I notice things others miss and have an exceptional talent for noting anomalies, testing them for repeatability and documenting them in detail.