Source date intervals permitted both temperature slope signs in two eastern US camera samples in 2016-2023

We tested date uncertainty in a prior spring greening study. We reused 101 site-years at eight eastern US camera sites in 2008-2023. Four separate models used site effects and site trends. Each date could vary within its source uncertainty interval. Exact temperature slope ranges were -2.15 to -0.89 and -4.48 to -2.51 days per C in the early northern and southern samples. Later ranges were -1.46 to +0.51 and -2.53 to +0.41. Thus both later samples permit either slope sign under independent date changes. Three-day dates gave the same sign result. A shared annual date error kept the later southern one-day range below zero, which shows dependence on the error model. These are fixed-sample sensitivity bounds, not confidence intervals. Source date intervals are estimates, not known limits on true dates. Sparse selected sites, missing records and coarse weather limit use. We do not test pollution, weather extremes or a causal climate effect. Code, source hashes, exact bounds, checks and a figure are included.