The past few years I've been tracking the accuracy of the Mock Composite draft site, which aggregates mock draft data from 180 big boards and over 1,300 first round mock drafts. Typically the first round has been pretty accurate - the past two drafts they hit on 27 of the 32 first rounders for example, with most of the misses getting drafted in the 2nd round, with the major exceptions of Shedeur Sanders last year and Jermond McCoy this year.
Below is this year's data in table form (I had to wait until McCoy was picked - he was mocked at 17 but ended up 101 or fourth round).
A yellow background in the 'Mock' column means those five players were drafted in round one but mocked lower (Banks mocked 44 or round 3 but drafted 18 for example). A blue background in the 'NFL draft' column is for the five guys mocked round 1 but drafted later. Three were picked early in round 2, a fourth late in round 2 and McCoy (coming back from injury) slipped into round 4, similar to what happened with Sanders last year (minus the injury excuse). So most of the mock's misses were still reasonably close.
'Delta' column shows the difference between mock and actual slot, with red indicating the mock was too optimistic. The red 59 at the bottom is the sum of these. Minus 59 means the average error for 37 players was less than 2 spots, which is impressive.
'abs delta' column adds the absolute errors, so plus seven and minus 7 would be zero in the 'Delta' column, but 14 here. If you divide the number (345) by the number of players (37) the average error was 9.3 or less than 1/3 a round. Scanning that column there is only one number higher than 32, meaning 36 or the 37 players were mocked within one round of where they were taken.
I also added the 247 Composite ranking for the 32 first rounders (average 447) and the star rankings 3.72 or 3++ in the Hamilton Metric.
Basically this idea of doing a composite seems to give pretty accurate results for round one.
I also am tracking where the Texas players are taken ... will have more on that later once the draft is done.