Now according to the old Code of Canon Law, anyone citing a Catholic bishop before a civil judge incurs automatic excommunication (canon 2341).Hence, according to the only Code of Canon Law which they themselves recognize, these five priests are excommunicated.”

—Bishop Williamson, Letters from the Rector - Volume 1: The Ridgefield Letters, June 5, 1984.

ABL's acceptance and promotion of Bugnini's & Montini's butchered Holy Week Liturgy.known as the1962 Missal would have made the Archbishop anathema according to St. Pope Pius V's Bull, Quo Primun.

Of the priests mentioned in the lawsuit. I don't believe any made such a Liturgical compromise?

Excerpt:

"...No man whatsoever may have permission to infringe these provisions containing our permission, statute, ordinance, mandate, precept, concession, indult, declaration, will, decree and prohibition, or be so rash as to oppose them. But if anyone should presume to attempt this, he must know that he will incur the wrath of Almighty God and of his Blessed Apostles Peter and Paul."

Given at Rome at St. Peters, in the year of the Incarnation of Our Lord 1570, on the day before the Ides of July, in the fifth year of our pontificate.

Source: https://lms.org.uk/quo-primum

2341  Si quis contra praescriptum can. 120 ausus fuerit ad iudicem laicuм trahere aliquem ex S. R. E. Cardinalibus vel Legatis Sedis Apostolicae, vel Officialibus maioribus Romanae Curiae ob negotia ad eorum munus pertinentia, vel Ordinarium proprium, contrahit ipso facto excommunicationem Sedi Apostolicae speciali modo reservatam; si alium Episcopum etiam mere titularem, vel Abbatem aut Praelatum nullius, vel aliquem ex supremis religionum iuris pontificii Superioribus, excommunicationem latae sententiae Sedi Apostolicae simpliciter reservatam; demum si, non obtenta ab Ordinario loci licentia, aliam personam privilegio fori fruentem, clericus quidem incurrit ipso facto in suspensionem ab officio reservatam Ordinario, laicus autem congruis poenis pro gravitate culpae a proprio Ordinario puniatur.

I am going to take his grace B. Williamsons side on this one.

Yes, I think that their out would be that technically Archbishop Lefebvre was not their superior, since he lacked jurisdiction ... except that 2341 itself is broader and would seem to include any bishop.

I would have to agree with Bishop Williamson's assessment.

So, in the first part, it says that if you bring a Cardinal, Legate of the Holy See, an Official of the Roman Curia, or your own Ordinary, you incur ipso facto excommunication reserved to the Holy See "in a special mode".  But, then it goes on that if you bring another bishop (abbot, etc.), "even merely a titular [bishop]" before such a judge, you incur excommunication reserved to the Holy See in a "simple form".  Now, I can't tell you the difference between excommunication reserved to the Holy See "speciali modo" vs. "simpliciter", but both are excommunication reserved to the Holy See somehow.

Nor does this one here required that the individual dragging them into (the force of "trahere") a lay court would have to be a cleric, as per that other version.