Impossible to say as each case is different involving different numbers of witnesses. The more witnesses the more discrepancies are likely to occur.
IMO In this case the police would only be interested in establishing whether or not JT walked up that road and saw a man carrying a child. The fact that she could describe Jez and Gerry talking - and knew Jez had a buggy with him would be far more pertinent to the police in respect of that imo - rather than the exact spot they were standing at the time she saw them.
(must dash now)
Absolute hokum. Your entire premise rests on the fact that the investigation, with no evidence of non involvement, has somehow excluded the parents from their suspicions or enquiries and moved on to Bundleman.
That's bad policing given that statistically family members or friends are more likely to be involved in a child's disappearance that a stranger.
It would be remiss of the Portuguese Police NOT to suspect and attempt to rule out the group.
Your belief is that they SHOULD be ruled out, but that's just because you happen to believe or like the Mccann's, but that isn't how investigations should or do work. Investigations cannot discriminate and rule people out just because potential perpetrators say they are innocent!
They have to provide the investigation with cast iron reasons why they should be ruled out. They hadn't done so, indeed their statements were so contradictory it added to the suspicion.
Hence the reconstruction, which would have served to either remove the doubt or increase it depending on what was shown to be true about what they said.
Further to that of course in relation to contradictions and it being normal for discrepancies. It is not normal for their to be wholesale changes to timelines IN UNISON between members of the group as there was regarding the Paraiso dinner and tennis match.
That is not normal.
Given all this it was and remains now perfectly correct for the PJ to try and get a handle on the truthfulness of the group's statements and actions by way of testing their version of events against real world conditions to attempt to discover if they were involve din the child's disappearance or not, as the people, statistically more likely to have carried out the crime.