Looks like what 'I think' would be a normal shift result (imo) while you changed >50% the overall TDS difference between replacement and tanked, 305-137=168ppm this reduction further reduced by the ratio of change to remaining tanked. Substrates with a high CEC will aid in holding up high readings until the charged ions bonded to the sub reach equilibrium releasing into the softer water. Fert dosing, declor products, anything added to the water increases tested TDS. This topic is above my tanking pay grade for a precise answer.
I use 100% RO for water changes and don't ratio mix tap/product, I prefer to replace evaporation or water change with near zero TDS water. Hobby grade chemical tests won't register GH/KH as anything but zero and TDS is 1 or 2ppm. Tracking tank parameters using an excel spread sheet my results are in a different format for reference. I don't normally record post WC TDS but test GH/KH and then add minerals for set point recording that value in the log. The following day I test TDS for a 'clean' value then dose my first post WC fert addition.
43g water column - 34gWC = 85%WC
B4WC TDS 190ppm, 5dGH, 3dKH, NO3 5ppm, PO4 1ppm
after WC 1dGH, 1.5dKH, NO3 & PO4 0.0ppm / added 32 grams of GH booster which should increase my tank by 3dGH.
Post testing TDS 177ppm, 4dGH, 2dKH
Do have a couple tracks in similar format to yours. All added water was <2ppmTDS (basically distilled).
35g water column - 28gWC = 80%WC
B4WC TDS 225ppm / post 98ppm
43g water column - 30gWC = 70%WC
B4WC TDS 182ppm / post 89ppm
43g water column - 32gWC = 75%WC
B4WC TDS 212ppm / post 52ppm
63g water column - 31gWC = 49%WC
B4WC 289ppm post 152ppm
120g water column - 76gWC = 63%WC
B4WC TDS 254ppm post 93ppm
120g water column - 65gWC = 54%WC
B4WC TDS 223ppm post 94ppm
I don't know if anything offered here helps or not