Thanks auv-ee. I had not previously seen the complete report and was not aware that it was in the public domain. I have only skimmed over it, but a lot of it is well beyond me I am afraid. It is certainly a very sophisticated attempt - perhaps even too complicated.
I plotted the location of the bodies when found against the time of discovery.
7780 3.57 9056 3.65 9504 3.7 9542 3.73 9554 3.74 9566 3.75 9640 3.73 9740 3.75 10963 4.04 10990 4.03 11015 4.06 11059 4.06 11110 4.08 11141 4.09 11970 4.25 12001 4.25 12047 4.25 12134 4.27 12161 4.27 12194 4.31 12246 4.31 12330 4.35 12330 4.35 12369 4.41 The first figure is the duration of time (minutes) that the body was in the water - from 0215 on the 1st until discovery. The 2nd figure is latitude (decimal).
The 1st body found (1155 on the 6th) is a bit of an outlier. The graph is reasonably linear for the bodies found on the subsequent days. However this 1st body is too far north. Possibly there was an error recording the position, although this is unlikely given the significance of this finding.
If you ignore this 1st body and then do a linear extrapolation from the subsequent bodies, you end up around 1.6N - I don't think anyone believes the aircraft will be found that far south.
So this suggests that the drift changed sometime around the 6th and the 7th, complicating the backtrack.
The other evidence for this change is they didn't find any bodies on the 8th until 1658 UTC. They found one on the 6th at 3.57 N. They found 7 on the 7th between 3.65 and 3.75 N. This limited data would suggest a fairly gradual drift. On the 8th they presumably went out to the same area and didn't find any bodies until late in the afternoon at 4.04N. This suggests they did not find bodies the next day where they expected them to be - the drift had changed (increased) carrying them 15 or so miles further north from the previous day. Maybe the weather was bad in the morning and precluded searching earlier in the day. If the weather was OK however, a likely explanation for not finding bodies early in the morning was that they were not where they expected them to be, and it took them time to re-establish contact with the group. 15 miles does not sound like much, but it is when looking for a body in the open ocean a long way off shore when aircraft have limited time overhead. It could easily take hours to re-establish contact. To me, this is evidence that the current was likely non-linear over this interval.
I have played around with a few graphs, and have also come up with a figure of about 2 30' N. Interestingly this is close (sort of) to Fluid Flow and Sam - however I suspect that mine is more of a "guess" than their estimate. The data is just too limited.
The authors of this drift analysis struggled also. Lots of assumptions. Look at the comment that "the impact could be further east if we have underestimated the wind effect on the bodies". For all their considerable best efforts, the conclusions are only as good as the assumptions and estimates that went into it.