Is access to previous access levels implied?

Drip-fed subscription builds 1 Unit (level) per month, member charged 9.97 per month, first month free.

As in...
Level 1 finite 1 month 0.00
Level 2 finite 1 month 9.97
Level 3 finite 1 month 9.97
Level 4 finite 1 month 9.97

During creation of Access Levels, are the access settings to the previous levels already implied in the settings for the plugin?

As in...
Level 1 = Unit 1
Level 2 = Unit 2 (and by implication Unit 1)

Or do I need to add the previous units to the next level?
As in....

Level 1 = Unit 1
Level 2 = Unit 1 + Unit 2
Level 3 = Unit 1 + Unit 2 + Unit 3
Level 4 = Unit 1 + Unit 2 + Unit 3 + Unit 4

Hope this makes sense!

Thank you!