“the execution of” vs “execution of”

Please, have a look at the following sentences:

1. Executing agency (also referred to as “executing entity”) shall mean the entity responsible for execution of UN-Women programme activities as defined in regulation 27.2.

2. The funds generated through the round tables should be allocated directly to UNDP, or to the United Nations and specialized agencies, or to the beneficiary Governments responsible for execution of these projects, in order to reduce the number of intermediaries and shorten time-lags.

3. The Executive Director of UNEP shall be responsible for the execution of the functions of UNEP under this MOU.

4. Judges responsible for the execution of sentences must be appointed; meanwhile, criminal judges must perform this function.

5. The manufacturer shall be responsible for the execution of the approved plan of remedial measures.

Could you please explain why the zero article is used in the first two sentences before the word “execution”, while in the other three sentences there is the definite article before the same word?