When I learned Vietnamese, the order of the tones in every dictionary (all my older ones) was

a á à ả ã ạ

Some of my newer dictionaries use the order you mention in above, but after twenty years of doing it one way, it's a little hard to change :)

There are also some differences in how initial consonant clusters are handled : does "thu" come before "tu" (in my older dictionaries "th" and "tr" are considered single "letters", kind of like c and ch in Spanish. I figured I would let this slide for now ...

Thanks again!