Those summertime highs are an interesting trend for sure. It’s a lot more intricate than the fact that we’re getting warmer overall. I wasn’t alive in 1977 but I don’t question it because it was taken at the same site and probably with similar methods to observations taken today.
I’m not sure of the official position of the NWS or others who study meteorology for a living on the older data or its accuracy, but I do know this. People on both sides of the aisle have politicized the non-political, scientific issue of climate change. As a result, even if the NWS did a quality control study and determined that the old data to be inaccurate, and put an asterisk next to it in the records, there would be an uproar about “artificially manufacturing or overstating climate change” or even “trying to rewrite history,” even if their reasons for doing so were legitimate. Therefore, the older data is here to stay. With that being said, we’re all free to use whatever data we want to come to whatever conclusion we like. I just choose to only use data from 1948 on because they’re the only numbers that I feel can give me an accurate comparison.