By my calculations, last year started slow in terms of sugar content too. I made 9 batches of syrup last year and my estimated sugar contents were as follows. Keep in mind I do not have a hydrometer and I deem my syrup finished by it's viscosity (as suggested by Rink Mann in his amazing book). My later batches of syrup were more thick than the others which could partly explain the observed lower sugar content values at that time.

Date Batch finished - ratio of sap to syrup - estimated sugar content
March 16, 2014 - 48.777 - 1.76
March 23, 2014 - 47.110 - 1.83
March 31, 2014 - 38.618 - 2.23
April 5, 2014 - 39.301 - 2.19
April 6, 2014 - 40.940 - 2.10
April 7, 2014 - 24.673 - 3.49
April 9, 2014 - 51.122 - 1.68
April 11, 2014 - 50.286 - 1.71
April 17, 2014 - 54.341 - 1.58