How do you know you they did not dye it?
There was dye in the system, bright green stuff around the cap of the HP valve. But as well all know the dye is utterly useless in actually diagnosing a leak, as always on the Omega the compressor is covered in crap and dye, the old 3.0 estate had green dye all over the place, yet the air-con never failed.
Recall your MV6 needing a yearly re-gas, I suspect this will be the same.
If dye was used - and the dye can generally only be seen properly with UV, but some are a fluorescent yellow now - then any leak would be obvious (under UV light if its UV dye). That's how I know they didn't put dye in it, or otherwise stringing you along
The MV6 needed almost
monthly regases purely because the national fast fit people don't know what they are doing. Look it to somebody who did, and low and behold, no further issues, despite nothing being replaced other than the refrig.