If Pope Benedict XVI did not do what the Code of Canon Law says to do, then it never happened... it was null and void. But whatever it was that Pope Benedict XVI did do, Pope Benedict XVI did not resign, or renounce "suo muneri" (his office). By the way, in and of itself, a "Declaratio" is not a "Renuntiatio." The two are distinct in nature.

"Quapropter bene conscius ponderis huius actus plena libertate declaro me ministerio Episcopi Romae, Successoris Sancti Petri, mihi per manus Cardinalium die 19 aprilis MMV commisso renuntiare ita ut a die 28 februarii MMXIII, hora 20, sedes Romae, sedes Sancti Petri vacet et Conclave ad eligendum novum Summum Pontificem ab his quibus competit convocandum esse." - Declaratio, die 11 mensis februarii MMXIII - Benedictus XVI | Benedictus XVI

"On which account, well aware of the weightiness of this act, I declare in full liberty, that I renounce the ministry [ministerio] of the Bishop of Rome, Successor of Saint Peter, committed to me through the hands of the Cardinals on April 19, 2005, so that on February 29, 2013, at 20:00 Roman Time [Sedes Romae], the see of Saint Peter be vacant, and that a Conclave to elect a new Supreme Pontiff be convoked by those whose duty it is [ab quibus competit]." - A.B.

"For this reason, and well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of Saint Peter, entrusted to me by the Cardinals on 19 April 2005, in such a way, that as from 28 February 2013, at 20:00 hours, the See of Rome, the See of Saint Peter, will be vacant and a Conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is." - Declaratio (11 February 2013) | BENEDICT XVI @Jared E Malone

Can. 332 § 2 - If it happens that the Roman Pontiff resigns his office, it is required for validity that the resignation is made freely and properly manifested but not that it is accepted by anyone.
Code of Canon Law - Book II - The People of God - Part II. (Cann. 330-367)
Can. 332 § 2 - Si contingat ut Romanus Pontifex muneri suo renuntiet, ad validitatem requiritur ut renuntiatio libere fiat et rite manifestetur, non vero ut a quopiam acceptetur.
Codex Iuris Canonici - Liber II (Cann. 204-746)

Can. 188 - A resignation made out of grave fear that is inflicted unjustly or out of malice, substantial error, or simony is invalid by the law itself.
Code of Canon Law - Title IX - Ecclesiastical Offices (Cann. 145-196)
Can. 188 - Renuntiatio ex metu gravi, iniuste incusso, dolo vel errore substantiali aut simoniace facta, ipso iure irrita est.
Codex Iuris Canonici - Liber I (Cann. 1-203)

Can. 17 - Ecclesiastical laws must be understood in accord with the proper meaning of the words considered in their text and context. If the meaning remains doubtful and obscure, recourse must be made to parallel places, if there are such, to the purpose and circumstances of the law, and to the mind of the legislator.
Code of Canon Law - Title I - Ecclesiastical Laws (Cann. 7-22)
Can. 17 - Leges ecclesiasticae intellegendae sunt secundum propriam verborum significationem in textu et contextu consideratam; quae si dubia et obscura manserit, ad locos parallelos, si qui sint, ad legis finem ac circumstantias et ad mentem legislatoris est recurrendum.
Codex Iuris Canonici - Liber I (Cann. 1-203) @Jared E Malone