The total transaction count (for progress estimation) is counted as the known count at the last checkpoint, plus an estimated number per day.

The last checkpoint is now 996 days ago, and its estimated 60000 transactions per day leads to a total estimate of 96M transactions, while the real number is around 183M.

Fix this by updating the count, timestamp, and rate of transactions... with or without adding a new checkpoint.
* 
 * Call without cs_main held.
 *
 * @param[in]   pblock  The block we want to process.
 * @param[in]   fForceProcessing Process this block even if unrequested; used for non-network block sources and whitelisted peers.
 * @param[out]  fNewBlock A boolean which is set to indicate if the block was first received via this call
 * @return True if state.IsValid()
 */
bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<const CBlock> pblock, bool fForceProcessing, bool* fNewBlock);
/**
 * Process incoming block headers.
 *
 * Call without cs_main held.
 *
 * @param[in]  block The block headers themselves
 * @param[out] state This may be set to an Error state if any error occurred processing them
 * @param[in]  chainparams The params for the chain we want to connect to
 * @param[out] ppindex If set, the pointer will be set to point to the last new block index object for the given headers
 */
bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex=NULL);
bool CheckDiskSpace(uint64_t nAdditionalBytes = 0);
FILE* OpenBlockFile(const CDiskBlockPos &pos, bool fReadOnly = false);
FILE* OpenUndoFile(const CDiskBlockPos &pos, bool fReadOnly = false);
boost::filesystem::path GetBlockPosFilename(const CDiskBlockPos &pos, const char *prefix);
bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, CDiskBlockPos *dbp = NULL);
bool InitBlockIndex(const CChainParams& chainparams);
bool LoadBlockIndex(const CChainParams& chainparams);
void UnloadBlockIndex();
void ThreadScriptCheck();
bool IsInitialBlockDownload();