Happy New Year folks!!!
It’s pretty obvious that the ending was retooled.
The short scene of R2-D2 and C3-PO on Yavin saying “the’re going to Scariff” Obviously the droids were not going to Scariff they were going to Tattooine. As was clearly explained earlier by Bail Organa when he talks to Mon Mothma.
“Skyhook come in Skyhook!”
That whole Darth Vader Slasher Sequence was an insert and the Tantive IV was combined with Raddus ship for more dramatic impact.
I am guessing but it’s more likely that a transmission was Beamed from Raddus ship or there is concept art for a half moon ship that would have probably beamed the transmission on. Basically you are watching a re-jigged ending but the remnants of the alternate (original) ending were still left in the film so far as C3-P0 and R2-D2 Mon Mothma and Bail Organa and him sending Leia to get Obi-wan.
This ending totally contradicts these earlier scenes before the Vader slashing his way through the corridor.
The Brutal Vader scene with Saw (Flashback) was cut and replaced with Brutal Vader on the Tantive.