uint256 diffBlock = currentBlock - priceInfo.updatedAt;
if (diffBlock <= config.expirationPeriod) {
    validPriceList[validNum] = priceInfo.twap;
    validNum++;
}
//expirationPeriod at least the interval of client to feed data(currently 6h=21600s/12=1800 in mainnet)
//we do not accept price lags behind to much
uint128 constant EXPIRATION_PERIOD = 1800;
