The glass lining is more like a paint that is then heated to crystalize on the inside. Normally, a cosmetic dent on the outside doesn't dent the inner, water-holding tank. There's a layer of insulation between the inner and outer walls...the thing is probably okay. I'd be more concerned about a crack in the power vent. If it fell on a plug sticking out, that may have cracked the lining around it. Are they all still sticking out straight?
You can go to the government website (listed on the yellow tag) to read the test procedure. It is for a 'typical' family and use. Just like any average, few people match the average.
Depending on where you live, you may be required to install a tempering valve on the hot water outlet. And, if you're going to think about running it at 155, you MUST do it for safety purposes. Both a tempering valve and a vacuum breaker are required on any WH install where I live. This can add some extra costs and complexity to the install if yours does not currently have these.