Other things cross “section boundaries” – e.g. the 3-month period in the Part 4 consent to treatment provisions, and the 6-month period period for references – so I can see the attraction of wanting this period to as well. But I think construing the 3-year rule to take into account prior detention isn’t the most natural reading and could lead to (I think) obviously unintended consequences, like a reference for a hospital order patient before or around the 6-month point.
You could maybe get a definitive answer by demanding a 3-year reference “early”, then judicially reviewing the hospital managers’ refusal or appealing the tribunal’s decision that it lacks jurisdiction.
I can see what you mean by the different nature of the court and the tribunal in the ECHR context, but look at what was said in De Wilde (mentioned by @Richard_Rook in Tribunal applications in first six months of hospital order - #4 by Richard_Rook):
Where the decision depriving a person of his liberty is one taken by an administrative body, there is no doubt that Article 5 (4) (art. 5-4) obliges the Contracting States to make available to the person detained a right of recourse to a court; but there is nothing to indicate that the same applies when the decision is made by a court at the close of judicial proceedings. In the latter case the supervision required by Article 5 (4) (art. 5-4) is incorporated in the decision; this is so, for example, where a sentence of imprisonment is pronounced after “conviction by a competent court” (Article 5 (1) (a) of the Convention) (art. 5-1-a).
If the patient can’t or won’t make an application then the hospital managers should (and others might) request a s67 reference. The Code of Practice says:
37.45 Hospital managers should consider asking the Secretary of State to make a reference in respect of any patients whose rights under article 5(4) of the ECHR might otherwise be at risk of being violated because they are unable (for whatever reason) to have their cases considered by the Tribunal speedily following their initial detention or at reasonable intervals afterwards.
37.46 In particular, they should normally seek such a reference in any case where:
- a patient’s detention under section 2 has been extended under section 29 of the Act pending the outcome of an application to the county court for the displacement of their nearest relative
- the patient lacks the capacity to request a reference, or
- either the patient’s case has never been considered by the Tribunal, or a significant period has passed since it was last considered.