Infallibility (Marauder's Map)

[brainattic]

No: HPFGUIDX 74578

I've been re-reading PoA and I just realised that, since Lupin used 
the Marauder's Map to follow Harry & co.'s movements from Hagrid's 
hut to the Shrieking Shack, shouldn't he have been able to see Future 
Harry and Future Hermione as well? 

Lupin says that he had an inkling that Harry & Co. would go visit 
Hagrid before Buckbeak was executed, so he monitored their movements 
all the way to Hagrid's house. But at the same time they left the 
house after the executioner arrived, Future Harry & Hermione (after 
using the Time Turner) were freeing Buckbeak. Lupin claims the Map's 
fairly infallible -- i.e., not to be fooled by cloaks or 
transformations. Wouldn't Lupin have noticed that there were four 
little dots moving around the periphery, two labeled Harry Potter and 
two labeled Hermione Granger? Or does Lupin just have extreme tunnel 
vision? 

Sorry, I know everybody's talking about OoTP right now. If this has 
been discussed before, can you point me to the thread?