In this case it is easy to suspect that both Robinson and the FAA believed that between all the Astros having to get the hydraulic refit and the 12 year overhaul cycle, most owners would ultimately get the bladders by default. Since essentially all the Astros had to go to the Robinson factory for the refit Robinson would have forced that issue. But some number of Ravens built between when they were introduced in 2000 and the 2010 SB, even potentially having undergone more than one overhaul cycle, don't have them because the owners didn't/don't want to incur the cost. The sheet metal work, and the subsequent requirement for a paint job, drives the cost up quite a bit. Not saying it's right or wrong. It does make you wonder exactly how many are left like that.