Recent advancements in Low-Gain Avalanche Diode (LGAD) architectures, including resistive and compensated designs, highlight the need for a precise understanding of donor removal at high donor concentrations to optimize their performance after irradiation. A method based on the variation of sheet resistance with fluence, measured through van der Pauw test structures, has been introduced to extract doping-removal coefficients. This approach was applied to resistive LGAD samples to quantify donor removal in the donor-doped resistive collection layer (NPLUS). Test structures from the RSD2 batch, manufactured by Fondazione Bruno Kessler with varying NPLUS doses, were irradiated up to 5.0 $\times$ 10$^{15}$ 1 MeV n$_{\text{eq}}$/cm$^2$ at the JSI TRIGA reactor, and donor removal coefficients were experimentally determined using this method. In this contribution, TCAD simulations are used to validate the experimental results and to confirm the reliability of the van der Pauw-based extraction method.