Because there are no regulations that address in-chamber autoclave validations, the answer would technically be yes you can. What I can tell you from my own experience is that only validating one would be a mistake. I have personally experienced, on multiple occasions, a situation where identical autoclaves that were fed steam from the same supply had vastly different results.
One would meet all of the parameters set forth in AAMI ST79 and the other would not meet all of the parameters. On each of those “silent failures”, the department had no indication that this autoclave was not meeting all of the parameters required by ST79. The data collected during the validation was used to determine the causes of these failures. In some cases, the steam supply lines were not being maintained properly, in another, the steam supply lines were routed improperly causing a “dead head” where the steam became stagnant and began to condensate.
Other potential causes are valves or gaskets in the autoclave may be in need of adjustment, calibration, or replacement. Practically every Sterile Processing Department has certain autoclaves that get used more often than other autoclaves in the department and many departments have different model autoclaves that were installed at different times. All of these factors make it imperative that all autoclaves be validated at the very least on an annual basis.