yyyymm_calc(202412, add_month = 1)
yyyymm_calc(c(202411,202412,202501), add_month = -1, add_year = 1)
yyyymm_calc(202410, diff_to = 202501)
yyyymm_calc(c(202411,202412,202501,202502), diff_to = 202501)
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