Analysis of information sources in references of the Wikipedia article "Kota Kinabalu" in Malay language version.
About 1967, they added E as a prefix for new registrations in Sabah (for East Malaysia) (about 1967). and at unknown later date, added an S suffix to existing plates.
Pada masa ini hospital Queen Elizabeth ialah hospital terbesar di negeri Sabah. Ia pusat rujukan untuk semua hospital daerah yang mengandungi 589 katil.CS1 maint: unrecognized language (link)
Actually in Sabah, there were no Malays. You were either Bajau, or Murut, or Orang Sungai. The closest to Malays were the Brunei Malays because they were originally from Brunei before settling in Sabah
About 1967, they added E as a prefix for new registrations in Sabah (for East Malaysia) (about 1967). and at unknown later date, added an S suffix to existing plates.