One who heard these words when they were first spoken, Peter, says :
... the appearing of Jesus Christ, whom having not seen, ye love; in whom, though now ye see him not, yet believing, ye rejoice with joy unspeakable and full of glory: [1 Peter 1:7,8.
Loving the Lord Jesus and believing in him, results in joy unspeakable and full of glory. That is the experience of those who follow the commands of Jesus : to believe in his name and to love one another. Being justified (through faith) they receive the indwelling of the Person of the Holy Spirit. His Divine Presence is holiness and thus the indwelt know true joy, within.
Certainly, Peter did as you ask (Did the disciples show this complete joy?). So did John and we have John's record and his epistles. So did Matthew. And Philip, as we see in Acts. Jude also, and James, from their epistles. Thomas, too, though he doubted, yet he rejoiced when he saw the Lord. Yes, indeed they did.
The knowledge of the forgiveness of sins (not just the reading about it, but the actual experience of knowing the personal forgiveness of God, himself) brings joy and release and results in love :
Wherefore I say unto thee, Her sins, which are many, are forgiven; for she loved much: but to whom little is forgiven, the same loveth little. [Luke 7:47 KJV]
Jesus required no other obedience than love :
If ye love me, keep my commandments. [John 14:15 KJV]
And this is no burden, for :
... this is the love of God, that we keep his commandments: and his commandments are not grievous. [1 John 5:3 KJV]
For it is clear what are the commandments of God to those who follow Jesus :
And this is his commandment, That we should believe on the name of his Son Jesus Christ, and love one another, as he gave us commandment. [1 John 3:23 KJV]
Then is 'joy complete' when we love him, believe on him, love his own sheep, and keep those unburdensome instructions that are recorded in his word by his own chosen apostles.
Then is 'his joy' in us, if we so follow.
For his joy was to keep the Father's command :
And I know that his commandment is life everlasting: [John 12:50 KJV]
Life everlasting is the commandment of the Father to his only begotten Son. And love and faith are the commandment of the only begotten to those who follow him.