Many engineers use series of drawings, ie: E100, E101, E102, E-200, E201, E202, E-300, E301, E302, etc. in lieu of E1, E2, E3, E4 etc.

So before separating the drawings to do your take-off, in the lower right hand corner of the drawing block, number the drawings: 1,2,3,4,5 and so forth.

When you want to put the drawings back in their proper order, this will make the task simple. On small projects, probably would not be necessary; but on projects with twenty or more drawings, probably a good idea.