For 1974 there were a number of Business Strike variations. Each of the three mints produced a Large Date and a Small Date Variation. However, 1974 coins are not usually recognized with those differences as they are for 1960-P and D, 1970-S, and 1982-P and D. A complete Lincoln Cent Business Strike collection should ignore this oversight and include both.
From the San Francisco mint two different mintmark styles were produced for both Busimess Strike and Proof coins. For 1979 and 1981 the two different mintmark styles produced in those years are recognized and assigned a Type I and a Type II designation. Perhaps the same should be done for the two 1974 Proof coin mintmark style variations. Early in the year the same S style as in prior years was used which can be labeled as the Tall S or MMS-008 as identified by. Later in the year the same S style to be used in subsequent years, call it the Blob S or MMS-009 was used. I suggest that the Tall S should be called the 1974 Type I and the Blob S should be called the 1974 Type II. A complete Lincoln Cent Proof collection should include both.
1974 Tall S business strike coins all have the Large Date. 1974 Blob S Business Strike coins all have a Small Date. Both 1974 Proof mintmark variations have the Large Date.
The best way I have found to tell the difference between the Large and Small Dates is by looking at the triangular hole inside the 4 of 1974. On a Small Date it is slightly but noticeably taller than it is wide. On a Large Date it is equally wide as it is tall.
Let's start with an examination of the Business Strike variations.
San Francisco Mint
The date style is sufficiently different such that 1974 should be added to 1960, 1970, and 1982 as Lincoln Cent years recognized to have Large and Small Date variations.
Now let's look at the Proof coins to demonstrate that 1974 Proofs should also have Type I and Type II status in addition to 1979 and 1981. Both 1974 mintmark variations have the Large Date style.