The value may be any ECC recovery. SNR gets lower as density increases, so ECC is constantly being used, as some portion of each read or write may have some defects. The kind of recovery you'd want to worry about is recovery that needed read retries, which you may or may not be able to glean from SMART values.
It's probably like the load cycle count for WD 3.5" Green and 2.5" Blue drives: ever-increasing values may just be a sign of continued normal operation.
When it has to mark sectors as bad, and/or re-allocate, that's when you should worry.
"The computer can't tell you the emotional story. It can give you the exact mathematical design, but what's missing is the eyebrows." - Frank Zappa