It doesn't matter what evidence we dig up from our limited resources and press inventions but the police investigated all this and stated in their final report to the public prosecutor that the checks story was suspect. The public prosecutors thereafter stated it as fact in their archiving report to the Attorney General. The links are all there at the top of page 1 so I suggest you read them.
We don't need to prove anything, the proper authorities in Portugal already did that.
On page 2412, is the interview with PAMELA FENN, who relates several details, of which, though not clarifying the facts, are elucidating.
PAMELA FENN lives on the first floor of the residential block, above the apartment occupied by the McCANN family. She related that, on 1 May 2007, two days before the disappearance, at about 22h30, she heard a child crying, which by the sound was MADELEINE. The child continued weeping for one hour and 15 minutes, until the parent’s arrival (she heard the door sounds), at about 23h45. This witness places in cause the allegation (by the parents) of the daily routine of visits every 30 minutes to check the children who had been left on their own.Mrs Fenn never said that it was Madeleine. She was asked if, in her view, the crying came from a child two years or younger (at least that is how it was written down in the statement). What was she actually asked? Was it phrased like that when she was asked? Or was she asked if it could have been an infant / baby or whatever other term to distinguish very young children?
There are also numerous questions as to why there is no mention of the two gates, whether she wore a hearing aid (as elderly people often do), etc.
I find it totally plausible that she'd got a bit confused and heard one or more young children crying at some point from any apartment, heard a patio door sliding at some point, but heard whichever twin had woken up later than her recollection and possibly Madeleine calling out as she toddled over to sleep with her parents that night.
Wihout further corroboration it's impossible to know whether her account is accurate or not (particularly 3 months later and noted in reported speech).