"Only in this case did it not fully yield the expected results"
Normally you would put the verb after 'it': "Only in this case it did not fully yield the expected results"
However, the inverted structure, as with all inverted structures, is used for emphasis - in this case to emphasis the negative.
Contextually this might be done if the the result was unexpected/you were trying to force a different result e.g., something returned the same results nine times, you change a variable and then you get a different result.
As a general rule of thumb the adverb should go as close as possible before the verb, so the position of 'fully' is OK with me.
Re: 'the'. Don't use 'the' with noun + No.1 / No.2 etc