Is one preposition enough for multiple months?

A colleague of mine has written her thesis and requested me to read and correct its grammar. I have seen some sentences like

The maximum deviation of the concentration values were obtained in the growing season, especially in May, in July, in August and in September.

As you see there is one 'in' for each month. I think that one preposition would be enough for all:

The maximum deviation of the concentration values were obtained in the growing season, especially in May, July, August and September.

Which one is more suitable?

Solution 1:

Omitting subsequent inclusions of the preposition is best when all the elements are objects of the same preposition. You would only supply prepositions with each list element if two or more list elements are the objects of different prepositions, such as saying, "I found toys all throughout the house--under the bed, on top of the refrigerator, and even behind the oven!"