they are hydraulic? So not interconnected?
127RG & 182RG landing gear are independent hydraulic. 177RG mains are hydraulic interconnected. So, locks notwithstanding, a 172RG or 182RG with an unusual hydraulic failure could have one down, the other not. For a 177RG, it would require a mechanical failure to result in asymmetric extension. There was an AD on the main landing gear forgings of the 182RG, but unlikely that defect was a factor in this event, it related to leaking and brakes, rather than total failure.
If found the 172RG, and 182RG main landing gear system much more "definite" and confident on operation than that of the 177RG,