Lack of attic sprinklers is a weakness in 13R systems. NFPA 13R states that the standard is intended to prevent flashover in the room where a fire originates (1.2.2), and attics are not required to be sprinklered (6.6.6) because few fatal fires originate in attics (A.1.2). Although such a partial sprinkler system may provide more safety than an unsprinklered building, it also provides a false sense of security because it can still be overwhelmed by a fire which starts outside of an apartment and spreads rapidly through a combustible attic.
It's been a few years since the last one, but we had several big fires in 13R sprinklered apartments without attic sprinklers here in Richmond. The fires started outside, got into the attic through the eaves, then spread throughout the entire attic. Somebody noticed the fires and knocked on doors to tell occupants to get out. They got out before the roof & ceilings started collapsing. Some lacked draft stops in the attic, and the draft stops often were like swiss cheese since it takes a 12" hole to run a 1/4" cat 6 or coax cable. I submitted code change proposals to the state which would require heat detectors in unsprinklered attics and noncombustible draft stops between every unit. They were turned down because the code people claimed these changes would be for property safety rather than life safety.