At a minimum, help text should note this. This is true for things like addwitnessaddress especially.
+ HelpExampleRpc("rescanblockchain", "100000 120000")
            );
    }
    LOCK2(cs_main, pwallet->cs_wallet);
    CBlockIndex *pindexStart = chainActive.Genesis();
    CBlockIndex *pindexStop = nullptr;
    if (!request.params[0].isNull()) {
        pindexStart = chainActive[request.params[0].get_int()];
        if (!pindexStart) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid start_height");
        }
    }
    if (!request.params[1].isNull()) {
        pindexStop = chainActive[request.params[1].get_int()];
        if (!pindexStop) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid stop_height");
        }
        else if (pindexStop->nHeight < pindexStart->nHeight) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "stop_height must be greater then start_height");
        }
    }
    
    if (fPruneMode) {
        CBlockIndex *block = pindexStop ? pindexStop : chainActive.Tip();
        while (block && block->nHeight >= pindexStart->nHeight) {
            if (!(block->nStatus & BLOCK_HAVE_DATA)) {
                throw JSONRPCError(RPC_MISC_ERROR, "Can't rescan beyond pruned data. Use RPC call getblockchaininfo to determine your pruned height.");
            }
            block = block->pprev;
        }