Nearly all certificates have the mileage listed on them, but never the time. The NPT rides are much, much longer and generally don't have mileage listed since it takes months for most people to complete them. It's not A ride, it's many rides. The mileage means nothing to anyone except you, it's just a fun note of how many miles you did for that ride. Anything over the required miles for the cert means you earned that certificate.
As far as the eStore list of your rides, yes, it's a fun thing to see how many miles you covered for all of your combined certs, but you don't get any awards based upon miles covered, per se, just for the qualifying certificate rides you did to earn the various ME awards. All except the Silver are lifetime awards. You can get as many Silver Mile Eaters as you submit for, (and do the rides for in that 12 month period). The other ME awards are about xx number of certificate rides and x(x) number of Gold or Extreme level rides, not the number of actual miles you rode.
As far as the eStore list of your rides, yes, it's a fun thing to see how many miles you covered for all of your combined certs, but you don't get any awards based upon miles covered, per se, just for the qualifying certificate rides you did to earn the various ME awards. All except the Silver are lifetime awards. You can get as many Silver Mile Eaters as you submit for, (and do the rides for in that 12 month period). The other ME awards are about xx number of certificate rides and x(x) number of Gold or Extreme level rides, not the number of actual miles you rode.