Despite most sources tell that the storage type in stata should not matter, it is worth checking whether this is the case for your dataset. I just came across a situation where two identically constructed datasets (one stored in default type (float) and one stored in double) generated different output. Also before that i encountered a problem with person identifiers in the GSOEP if using the default data storage. If your dataset is not huge (with the GSOEP it still works quite ok) it might be worth to take the safe side and use
set type double
before you assemble your data set. This saves the data in the most precise way stata offers.