Of course, it is always up to the field as to what they will personally choose to fill or not. But, the DOT regulations are set forth by the government.
The requalifying requirements of any cylinder are specific to the DOT specification and/or exemption to which the cylinder was manufactured. The DOT specification and/or exemption number are stamped on the crown of the cylinder. Cylinders manufactured by Catalina Cylinders are marked with "M4002" on the crown of the cylinders. Cylinders manufactured by Catalina Cylinders Cliff Impact Division are marked with "CLIFFDIV" on the crown of the cylinder.
DOT-3AL Cylinders "2 by 2 rule" (Catalina Cylinders Cliff Impact Division only)
Requalification not required per the note under table 1 in 49CFR part 180.205. The note reads, "Any cylinder not exceeding two (2) inches in outside diameter and less than two (2) feet in length is exempt from volumetric expansion testing."
So, if the tank in question is under 2" in diameter and produced by the Cliff Impact Division of Catalina Cylinders, then it doesn't have to be re-hydro'd per government regulations.
Here's the official link direct from the government: http://www.gpo.gov/fdsys/pkg/CFR-200...sec180-207.pdf
It's under Table 1 as Note /1
Again, as I mentioned earlier, a field can always refuse to fill a vessel, regardless of the regulations.