Recently, I have been reading books written in the 30’s and the 40’s and something that came to my attention was the frequency of “alright/all right” in them. So I did the next step to investigate my suspicion and used Ngram to see if by any chance my observation made any sense. Well this is what I got.

https://books.google.com/ngrams/interactive_chart?content=all+right%2Balright&case_insensitive=on&year_start=1900&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2C(all%20right%20%2B%20alright)%3B%2Cc0

Obviously, it is not a definitive evidence, but it seems that “all right” was much more popular in the written English of the early 20th century.