Currently, when a lead is modified, the lead score is updated with the score of the condition(s) that was met when the lead was initially created/saved. It is not re-evaluating/recalculating the whole score model for the lead which results in discrepancy. It will just add on top of the previous score.
If all of the Lead details were filled at the time of creation, there is a chance that you will get the correct score, but this behavior is a problem because we don't expect the users to always have the complete details for the Lead at the time of creation.
Examples:
Number field condition:
RULE 1
IF CONDITION: For lead profile Where numberoflocations < "20"
THEN ACTION: Add 10 points
RULE 2
IF CONDITION: For lead profile Where numberoflocations >= "20"
THEN ACTION: Add 94 points
Scenario: Sales rep creates a lead where "numberoflocations" is null (null is assumed 0!) or "5" and save. Now the score is 10 points. If the sales rep goes back to the same lead and modify "numberoflocations" to "25" and save, the score will be "104". That is not an accurate score.

Optionset field condition:
RULE 1
IF CONDITION: For lead profile Where paidmediavaluerange = "624300000"
THEN ACTION: Add 10 points
RULE 2
IF CONDITION: For lead profile Where paidmediavaluerange = "624300001"
THEN ACTION: Add 20 points
Scenario: Sales rep creates a lead where "paidmediavaluerange " is "624300000" and save. Now the score is 10 points. If the sales rep goes back to the same lead and modify "paidmediavaluerange " to "624300001" and save, the score will be "30". That is not an accurate score.
Please modify this behavior so the lead score is completely re-evaluated/calculated when the record is modified.