The phrase up to is used to sort things into two groups based on their relationship to a criterion. The difficulty arises when the criterion to which up to refers consists of something that has a duration or value in itself, different from the values on either side of it.
Consider examples in which the criterion has no such distinct value
He was happy up to the moment he died.
Up to takeoff, the rocket is tethered to the launch pad.
Generally people consider the moment of death to have no duration. Dead or not-dead. Before death, happy; after death, not (or not determinable). The rocket is attached or not attached.
When the criterion has its own point on the scale, the use of up to becomes ambiguous (unless further qualified)
We will give dispensations for people earning up to $1000.
They are accepting applications up to July 1.
People who are up to 4 foot 6 inches tall are banned from the roller coaster.
What about people who earn exactly $1000? Those who apply on July 1? The 4 foot 6 inch daredevil?
As @Janus Bahs Jacquet suggests, the means of eliminating the ambiguity is to indicate whether the criterion value is included or excluded from the partition.
We will give dispensations for people earning up to and including $1000.
They are accepting applications up to, but not including, July 1.
People who are up to and including 4 foot 6 inches tall are banned from the roller coaster.
An alternative is to use under or over, before and after (or beyond)
We will give dispensations for people earning under $1001. [Note the change in amount]
They are accepting applications before July 1.
People who are under 4 foot 7 inches tall are banned from the roller coaster. [Again a change in value; this assumes most people report height in full inches].
The term until shares the same ambiguities with up to.