I don't think it has much to do with Julian vs Gregorian calendar (which is more about months and leap years) - I think this is just what is called a day of year calendar - readily available on line for any given year. The date it corresponds to will vary depending on Julian or Gregorian - but mostly we are using Gregorian so easy to look up.
https://www.esrl.noaa.gov/gmd/grad/neubrew/Calendar.jsp
Back to my concern though - is 8 weeks a tad elderly. I might try and clear some space in the freezer for some of it. My usual storage is in a galvanized bin in the Chicken Palace, but with temperatures in the '90s that feels like it will go off quite fast.