Texas Manifest Coding

Has anyone researched the coding notation on a Texas Manifest written years later on the same manifest? I'm curious as to what this means ( see bottom writing on attachment). I'm hoping it means my grandfather was alive all through 1954. The last record I found of him is dated 1919.

912/3 121: I - 404 lwn - San Antonio 9/15/52

I have similar coding on the bottom of my grandmother's 1919 manifest listing a date of 1932 and "Dallas".... and she was actually living in Dallas at that particular time noted.